Maybe plaster bandages would be easiest. Vaseline up and apply. Be very careful though because plaster is exothermic when it cures. Don't apply too much at once - if you do, you could burn yourself.
Most times when body parts are cast, the material used is Alginate, with additional support of plaster bandages. Alginate does shrink a bit and it is quite brittle so it will not survive many casts.
